1. Field of the Invention
This invention relates to opto-mechanical steering devices for thermal imaging systems which project the field of view of the scanner mechanism of the thermal imaging system over a wide field of search.
2. Description of the Prior Art
Presently there exists many thermal imaging systems designed to convert infrared radiation to visible radiation for viewing by an observer. The most common types of these thermal imaging systems are single framing thermographic cameras, downward looking single channel thermal mapping systems, and fast framing thermal imaging systems.
Fast framing thermal imaging systems comprise mechanically-scanning devices which convert radiation in the far infrared spectral region to visible radiation in real time and at an information rate (or frame rate) comparable to that of standard television. Such systems are commonly referred to as FLIR systems, the acronym for Forward Looking Infra-Red. Although the term FLIR originally implied an airborne system, it is now used to denote any fast framing thermal imager. Thermal imaging in a FLIR is produced by an optical system which collects, spectrally filters, and focuses the infrared scene radiation onto an optically scanned multi-element detector array. The elements of the detector array then convert the optical signals into analog electrical signals which are amplified and processed for display on a monitor such as a video monitor.
The function of the scanner mechanism in a FLIR is to move the image formed by the optical system in the plane of the detector array in such a way that the detectors disect the image sequentially and completely. The field of view of such scanning mechanisms are relatively narrow, usually from a few degrees to as much as ten degrees. Obviously, such narrow fields of view substantially inhibit the use of the FLIR in seeking out and locating various targets.
State-of-the-art steering devices designed to enable the FLIR to search a wide field of search typically comprise some type of a gimbal assembly, the axes of rotation of which are controlled by several stepping motors or the like. A joystick control is usually provided for controllably energizing the motors which in turn pivot the FLIR about the elevational and azimuthal axes of the gimbal assembly. More advanced steering devices have been developed which use computers to control the motors such that the FLIR automatically searches over prescribed fields of regards in preselected patterns.
The major disadvantage to these gimbal assemblies, more commonly referred to as platforms, is the fact that the entire FLIR must oscillate in the azimuthal and in the elevational directions in order to produce the desired search pattern. As is true with any oscillatory mechanism, a great amount of microphonics is produced which adversely affects the performance of the FLIR. Moreover, in order to produce just a single line scan the motor driving one axis of the platform must be capable of producing a high amount of torque sufficient to pivot the FLIR in one direction at a constant velocity, instantaneously decelerate the FLIR to a stop, and then instantaneously accelerate the FLIR to pivot the FLIR at a constant velocity in the opposite direction. Obviously, inasmuch as it is virtually impossible to instantaneously stop and start the movement of the FLIR, a uniform search rate cannot be achieved.
Another major disadvantage to steering mechanisms such as platforms is their inability to determine the exact position of the target. Typically, the direction cosines of the target may be computed by incorporating position detectors within the azimuthal and the elevational axes of the gimbal assembly of the platform. Unfortunately, there exists no device which may be used in conjunction with FLIRs to determine the distance to the target.
Therefore, it is an object of this invention to provide an apparatus and method which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the thermal imaging art.
Another object of this invention is to provide a steering mechanism for a thermal imaging system such as a FLIR which enables a FLIR to search over a wide field of search.
Another object of this invention is to provide a steering mechanism which obviates the need for platforms in which the entire thermal imaging system oscillates about the azimuthal and the elevational axes of the platforms.
Another object of this invention is to provide a steering mechanism which utilizes a pair of prisms which are individually controlled to produce preselected search patterns at any rate of scan within variable fields of regard over a wide field of search.
Another object of this invention is to provide a steering mechanism for a thermal imaging system including means for boresighting a rangefinder on the target viewed by the thermal imaging system.
Another object of this invention is to provide a steering mechanism for a thermal imaging system including means for boresighting a laser designator on the target viewed by the thermal imaging system for beam rider purposes.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner of modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.